(557b) Sonochemical Removal of Nitric Oxide from Flue Gases

The absorption of nitric oxide (NO) into water with simultaneous oxidation induced by ultrasonic irradiation at a fixed frequency of 20 kHz has been studied in a bubble column reactor at about room temperature. Factors studied include the flow rate of flue gas, intensity of ultrasound and effect of SO2 on the fractional conversion of NO. The concentration of NO in the inlet gas studied ranged from 50 to 1040 ppm while that of SO2 ranged from about 52 to 4930 ppm. The fractional conversions of NO were found to range from 60 to 85% while complete removal of SO2 was observed for all the inlet gas concentrations studied. In addition, the presence of low to moderate concentrations of SO2 in the inlet gas stream was found to enhance NO removal. Also, increasing ultrasonic intensity was observed to improve NO removal. NaCl in the concentration range of 0.01-0.5M was used as the salt to study the effect of ionic strength on the sonochemical removal of NO. At the low NaCl concentration (0.01M), the percent fractional removal of NO with initial concentration of 1040 ppm was enhanced significantly, whereas as the NaCl concentration increased the positive effects were less pronounced. The presence of about 2520 ppm SO2 in combination with 0.01M NaCl further enhanced NO removal. However, with NO initial concentration of 490 ppm, the addition of NaCl was detrimental to NO removal at all NaCl concentration levels. Combinative effect of sonication and chemical oxidation using 0.005-0.05M oxone was also studied. While the lower concentrations of HSO5- enhanced NO removal efficiency, higher concentrations were detrimental depending on the initial concentration of NO. Sonochemical oxidation pathways leading to nitrite, nitrate and sulfate formation are discussed. The results of this study suggest the feasibility of developing an innovative, cost-effective and low-temperature aqueous sonochemical scrubber to provide an environmentally conscious method for the control of NOx and SO2. This should reduce or eliminate chemical usage, resulting in minimal sludge and disposal problems and associated costs.